The present invention relates generally to servicing wells by the use of high density fluids. More particularly, the present invention relates to servicing wells by injecting as the high density fluid an aqueous solution of inorganic salts. The invention also relates to a method of preparing the aqueous solution.
In many wells, e.g., oil, gas, etc., it may be desirous to contain the formation pressure by employing a hydrostatic head. This may be needed during the squeezing of sand consolidation compositions, during perforation operations, during well shut-ins, during gravel packing, or the like. Many well-servicing fluids, sometimes referred to as completion or packer fluids, have been employed. These include, for example, drilling muds, salt water, brines, water, oil, ZnCl.sub.2 -CaCl.sub.2 solution, CaCl.sub.2 -CaBr.sub.2 solutions and the like.
However, drilling muds are not completely satisfactory as a well-servicing fluid because solids contained in the muds frequently tend to plug the formation. Although solutions of certain inorganic salts tend to be particle-free, there are other difficulties with their use as well-servicing fluids. For example, most inorganic salt solutions commonly used in wells in the Gulf Coast region of the United States are low density fluids having high crystallization temperatures (temperature at which solids first appear in the solution upon heating or cooling). For instance, sodium chloride-based fluids have a density of from 8.3 to about 9.8 pounds per gallon (ppg); solutions of calcium chloride have a density of from about 8.3 to about 11.5 ppg; solutions of calcium chloride and zinc chloride have a density of from about 11.5 to 14.0 ppg; and solutions of CaCl.sub.2 and CaBr.sub.2 have densities of from about 11.6 to about 15.1 ppg.
In recent years, deeper, high-pressure wells have resulted in a need for solids-free, well-servicing fluids having higher densities than are currently available. This is particularly true of wells in the Gulf of Mexico (offshore Louisiana). Here, hydrostatic pressures higher than normal often require well-servicing fluids having densities in excess of 15 pounds per gallon and crystallization points below about 50.degree. F.
It would therefore be desirable to develop a well-servicing fluid which had controllable densities in excess of about 15 pounds per gallon. Precipitation or settling out of solids during storage of the fluid or servicing of wells with the fluid should be avoided.